Composition for matte layer formation, release sheet using the same, and synthetic leather produced using said release sheet

ABSTRACT

There are provided a composition for matte layer formation suitable for the production of a matte synthetic leather having a matte surface with a high level of jet-blackness even without the practice of embossing, raising, etc., and a release sheet for the production of a matte synthetic leather by using the composition. The composition for matte layer formation suitable for the production of a matte synthetic leather comprises a thermosetting resin and a matting agent as indispensable components. The matting agent comprises one or at least two types of organic or/and inorganic porous fine particles. The porous fine particles have a mean particle diameter in the range of 0.5 to 20 μm and a specific surface area in the range of 1 to 1000 m 2 /g. The release sheet is produced by using the composition.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a release sheet for theproduction of a matte synthetic leather and a composition for theformation of the sheet. More particularly, the present invention relatesto a composition for matte layer formation suitable for the productionof a matte synthetic leather, which has a matte surface with a highlevel of jet-blackness without the practice of embossing, raising or thelike, and a release sheet for the production of a matte syntheticleather using the composition.

[0003] 2. Prior Art

[0004] According to one of conventional production processes ofsynthetic leathers, a synthetic leather is produced by coating acomposition for a synthetic leather, for example, a urethane resin, avinyl chloride resin, a polyamide resin, or an amino acid resin, on arelease sheet, drying or curing the synthetic leather coating, coatingan adhesive onto the dried or cured coating, laminating a backingfabric, such as a woven fabric, onto the adhesive coating, and thenseparating the release sheet from the synthetic leather compositioncoating. In this production process of a synthetic leather, syntheticleathers having various surface shapes can be produced by regulating thesurface form of the release sheet. Specifically, since the surface shapeof the synthetic leather is formed by transferring the surface form ofthe release sheet onto the synthetic leather, the regulation of thesurface form of the release sheet is necessary for the production of adesired synthetic leather.

[0005] One property required of synthetic leathers, particularly mattesynthetic leathers, is freedom from a faded color and is to bejet-black, that is, is to be matte.

[0006] For example, the following methods are known for the productionof these matte synthetic leathers. Specifically, in a conventionalmethod, a release sheet having concaves and convexes on its surface isproduced, for example, by utilizing an emboss roll as a chill roll inthe step of extrusion lamination in the production of the release sheetor by utilizing an emboss roll as a chill roll in the step of forming anapplication film in the case of the formation of the release sheet bythe application of an existing film, and the concave/convex shape of thesurface of the release sheet is transferred onto a synthetic leather. Inanother conventional method, a release sheet with an emboss of concavesand convexes is prepared by embossing the whole release sheet, and theconcave/convex shape of the surface of the release sheet is transferredonto a synthetic leather. In a further conventional method, a syntheticleather having a matte surface is produced by subjecting a syntheticleather to raising.

[0007] The synthetic leathers produced by these methods are suitablymatte. Since, however, the shape of fine concaves and convexes cannot beimparted by the embossing and the like, satisfactory jet-blacknesscannot be realized in synthetic leathers having a deep color, forexample, a black color. Further, in the methods wherein raising or thelike is carried out, a step should be additionally provided. Thisrenders the production process complicate and incurs increased cost.

[0008] On the other hand, as described in Japanese Patent Laid-Open No.158249/1985, a method for producing a matte synthetic leather, i.e., theso-called “synthetic leather with a matte tone,” has been developedwherein a composition for a release sheet with an inorganic pigment,such as silica or calcium carbonate, or a matting wax as a matting agentadded thereto is coated onto a substrate to form a release sheet.

[0009] In the release sheet formed by coating the composition with amatting agent added thereto, however, the addition of a predeterminedamount of an inorganic pigment or the like to the composition isnecessary for attaining satisfactory matte effect. However, when theamount of this additive added to the composition is excessively large,the so-called “drop of particles” wherein the matting agent is droppedfrom the release sheet takes place.

[0010] Further, increasing the amount of the matting agent added forimproving the matte effect causes aggregation of matting agentparticles, and the matting agent disadvantageously bleeds out on thesurface of the release sheet. Therefore, a release sheet having desiredfine concaves and convexes cannot be formed, and, further, a syntheticleather, which is matte and is jet-black, cannot be produced.

[0011] Further, in the composition, for a release sheet, containing fineparticles for matting purposes described in Japanese Patent Laid-OpenNo. 158249/1985 noted above, the incorporation of the fine particles canimpart a matte feel to some extent. However, it is difficult to providea synthetic leather which is jet-black without color fading.

[0012] The production of a matte synthetic leather by the conventionalmethods involves, besides the above problems, an additional problem thatthe addition of fine particles, which should be used as a matting agentfor the production of a matte synthetic leather, to the composition fora release sheet deteriorates the fluidity of the composition and thusdeteriorates the coatability of the composition.

[0013] Further, coating of a coating liquid onto a substrate having lowsmoothness to form a release sheet poses problems of deteriorated dryingproperties and lowered smoothness of the release sheet due to drying bystrong heating.

[0014] When conventional paper is used as the substrate, staticelectricity is likely to be generated at the time of the formation of arelease sheet. Further, in the production of a synthetic leather usingthis release sheet, since the step of separating the synthetic leatherfrom the release sheet should be provided, the generation of staticelectricity is unavoidable. Thus, the generation of static electricity,for example, at the time of the production of a release sheet poses aproblem of cracking of the surface of the release sheet and thesynthetic leather.

[0015] Accordingly, an object of the present invention is to provide acomposition for matte layer formation suitable for the production of amatte synthetic leather, which has a matte surface with a high level ofjet-blackness without the practice of embossing, raising or the like,and a release sheet for the production of a matte synthetic leatherusing the composition.

[0016] Another object of the present invention is to provide a releasesheet for the production of a matte synthetic leather, which releasesheet has excellent smoothness and can realize the production of a goodsynthetic leather free from defects such as cracking by virtue of thesuppression of the generation of static electricity.

SUMMARY OF THE INVENTION

[0017] In order to attain the above objects of the present invention,according to one aspect of the present invention, there is provided acomposition for matte layer formation, comprising a thermosetting resinand a matting agent as indispensable components, said matting agentcomprising one or at least two types of organic or/and inorganic porousfine particles, said porous fine particles having a mean particlediameter in the range of 0.5 to 20 μm and a specific surface area in therange of 1 to 1,000 m²/g. The production of a release sheet by using thecomposition containing a matting agent comprising such fine particlescan realize the production of a synthetic leather with a matte tonewhich is jet-black without color fading.

[0018] In a preferred embodiment of the present invention, the porousfine particles have been surface treated and have been homogeneouslydispersed in the composition for matte layer formation. More preferably,when the thermosetting resin is soluble in water, the surface treatmentis inorganic surface treatment, while, when the thermosetting resin isnonaqueous, the surface treatment is organic surface treatment. The useof the fine particles subjected to inorganic or organic surfacetreatment as the matting agent can improve the dispersibility of thefine particles in a coating liquid for matte layer formation. Therefore,even when the content of the fine particles in the coating liquid isincreased, the coatability of the coating liquid is not deteriorated.Further, since the fine particles are homogeneously dispersed in thecoating liquid, the coating liquid can form a matte layer having an evenconvex-concave surface.

[0019] Further, more preferably, the content of the porous fineparticles in the composition for matte layer formation is 5 to 50% byweight. When the content of the fine particles is in the above-definedrange, a matte synthetic leather can be produced which is uniform andhas a high level of jet-blackness. Particularly preferably, the porousfine particles are selected from silica, calcium carbonate, talc, and amixture containing at least one of said materials.

[0020] In a preferred embodiment, the composition for matte layerformation according to the present invention further contains a releaseagent. The incorporation of the release agent in the composition formatte layer formation can lower peeling resistance at the time of theseparation of the release sheet from the synthetic leather. Therefore,the release sheet can be easily separated from the synthetic leather.

[0021] According to another aspect of the present invention, there isprovided a first embodiment of the release sheet for the production of asynthetic leather according to the present invention, that is, a releasesheet for the production of a synthetic leather, comprising: a mattelayer formed by coating the above composition for matte layer formation;and a substrate for supporting the matte layer, said matte layer havinga fine concave-convex portion on its surface, said concave-convexportion having an arithmetical mean roughness (Ra) of 0.5 to 15 μm. Theuse of a release sheet having this surface shape can realize theproduction of a matte synthetic leather without the use of means such asembossing or raising.

[0022] According to still another aspect of the present invention, thereis provided a second embodiment of the release sheet for the productionof a synthetic leather according to the present invention, that is, arelease sheet for the production of a synthetic leather, comprising: amatte layer having fine concaves and convexes on its surface; and asubstrate for supporting the matte layer, said matte layer comprising areleasable resin layer, a releasable transparent resin being provided soas to stay on the bottom of the concaves in the concave-convex portion.The production of a synthetic leather using this release sheet can morereliably impart peach skin-like appearance and feel to the surface ofthe synthetic leather. Further, even in the repetition of the productionof synthetic leathers with different colors, since the releasabletransparent synthetic resin stays on the bottom of the concaves in thefine concaves and convexes, the release sheet has excellentreleasability. Therefore, the release sheet can be repeatedly used.

[0023] Further, in a preferred embodiment, the concave-convex portionhas an arithmetical mean roughness (Ra) of 0.5 to 15 μm, the meanspacing of profile irregularities (concaves and convexes) (Sm) in theconcave-convex portion is 0.5 to 10 μm, and the mean inclination (θa) ofsaid concaves and convexes is 45 degrees≦θa<90 degrees. The matte layerhaving this concave-convex surface can be formed by coating the abovecomposition for matte layer formation.

[0024] In the above first and second embodiments of the release sheetfor the production of a synthetic leather, a smoothing layer ispreferably provided between the matte layer and the substrate. Theprovision of the smoothing layer on the substrate can realize theproduction of a release sheet having a uniform fine concave-convexsurface without the influence of the surface of the substrate.

[0025] More preferably, the smoothing layer has been formed using acomposition having the same formulation as the above composition formatte layer formation except that the porous fine particles are absentin the composition. The use of this composition as the composition forsmoothing layer formation can form a smoothing layer which has increasedadhesion to the matte layer and thus can prevent interlaminar peeling.In particular, the incorporation of a leveling agent in the smoothinglayer can further improve the smoothness.

[0026] According to a further aspect of the present invention, there isprovided a third embodiment of the release sheet for the production of asynthetic leather according to the present invention, that is, a releasesheet for the production of a synthetic leather, said release sheetcomprising: a matte layer formed by coating the above composition formatte layer formation; and a substrate for supporting the matte layer,wherein said matte layer is a releasable resin layer having a multilayerstructure of at least two layers, all the releasable resin layersconstituting the multilayered matte layer except for at least the layerin contact with the surface of the substrate contain a release agentcomprising a silicone-modified resin or a silicone-containing resincomposition, and the content of the release agent is larger as thereleasable resin layer is closer to the surface of the matte layer. Theadoption of a multilayer structure of two or more layers in thereleasable resin layer is advantageous in that, even when the thicknessof the releasable resin layer should be increased due to low smoothnessof the substrate, the thickness of each layer can be reduced and, at thesame time, the layer near the substrate side can further improve thesmoothness. Therefore, a lot of time is not required for drying thecoating liquid. Further, in the layers other than the layer in contactwith the substrate, since the mixing ratio of the silicone-modifiedresin or silicone increases as the layer is closer to the surface of therelease sheet, a release sheet having excellent smoothness can beproduced without sacrificing the adhesion between the layers.

[0027] In the release sheet for the production of a synthetic leather ineach embodiment of the present invention, the surface resistivity of thesubstrate is preferably not more than 1.0×10¹² Ω. More preferably, thesubstrate contains an organic polymeric conductive agent and/or aninorganic conductive agent, or has, on any one side thereof, a coatingof the organic polymeric conductive agent and/or the inorganicconductive agent, and the content of the conductive agent is in therange of 0.05 to 3.00 g/m² based on the substrate. When the substratehas the above resistivity, the occurrence of static electricity can beprevented at the time of the production of a release sheet and at thetime of the production of a synthetic leather using the release sheet.

[0028] According to another aspect of the present invention, there isprovided a synthetic leather using the release sheet.

[0029] In a preferred embodiment, the synthetic leather of the presentinvention has been produced substantially without the practice ofembossing or/and raising.

[0030] According to a further aspect of the present invention, there isprovided a synthetic leather produced by using a release sheet, saidsynthetic leather having a surface arithmetical roughness (Ra) of 0.5 to15 μm and a 85-degree glossiness of 0.5 to 10%.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a typical cross-sectional view showing a firstembodiment of the release sheet for the production of a syntheticleather according to the present invention;

[0032]FIG. 2 is a typical cross-sectional view showing a secondembodiment of the release sheet for the production of a syntheticleather according to the present invention;

[0033]FIG. 3 is a typical cross-sectional view of a principal partillustrating a synthetic leather production process using a thirdembodiment of the release sheet for the production of a syntheticleather according to the present invention;

[0034]FIG. 4 is a typical cross-sectional view showing an example of thethird embodiment of the release sheet for the production of a syntheticleather according to the present invention;

[0035]FIG. 5 is a typical cross-sectional view showing another exampleof the third embodiment of the release sheet for the production of asynthetic leather according to the present invention;

[0036]FIG. 6 is an electron photomicrograph of the surface of a releasesheet for the production of a synthetic leather prepared in Example 1;and

[0037]FIG. 7 is an electron photomicrograph of the surface of a PVCleather 1 prepared in Example 1.

DETAILED DESCRIPTION OF THE INVENTION

[0038] Embodiments of the present invention will be described in moredetail with reference to the accompanying drawings.

[0039] The composition for the formation of a matte layer in a releasesheet according to the present invention will be first described. Thecomposition for matte layer formation according to the present inventioncomprises a thermosetting resin and a matting agent as indispensablecomponents. The matting agent comprises inorganic or organic porous fineparticles. Inorganic fine particles include fine particles of calciumcarbonate, kaolin, talc, clay, titanium oxide, zinc oxide, silica,alumina, magnesium hydroxide, aluminum hydroxide and the like. Organicfine particles include fine particles of melamine resin, polystyrene,polypropylene, ethylene tetrafluoride resin, silicone resin, starch,acrylic resin and the like. Since, however, the release sheet used inthe production of synthetic leathers is in many cases used under hightemperature conditions, the use of inorganic fine particles is suitablebecause of their excellent heat resistance. Among these inorganic fineparticles, silica, calcium carbonate, and talc are preferred because, asdescribed later, the specific surface area and the particle diametereach can be easily regulated as desired. Silica is particularlypreferred.

[0040] These fine particles should be porous. Specifically, in thepresent invention, fine particles having a specific surface area of 1 to1,000 m²/g are used. The pore diameter of the porous fine particles isabout 50 to 500 angstroms. Assuming that the particle diameter of thefine particles is identical, the specific surface area depends upon thepore diameter and the number of pores. That is, the specific surfacearea increases with reducing the pore diameter and increasing the numberof pores. In the porous fine particles having the above specific surfacearea, that is, a specific pore diameter and a specific number of pores,as the matting agent, light is irregularly reflected from pore portionsformed on the surface of the fine particles. Therefore, a syntheticleather onto which this surface shape has been transferred is jet-blackand is not seen as a faded color. On the other hand, in the case of fineparticles having a diameter of several μm, light scattering is mainlyMie scattering. Since, however, the Mie scattering does not depend uponthe wavelength, the object is seen white. For this reason, in syntheticleathers using a release sheet containing conventional fine particles,the surface is considered to be seen as a faded color. By contrast, inthe release sheet according to the present invention, by virtue of theincorporation of the above porous fine particles in the release sheet,light is also scattered in the pore portion (pore diameter: several tensof angstroms to several hundreds of angstroms) of the fine particles.This scattering is mainly Rayleigh scattering. In the Rayleighscattering, the intensity of scattered light depends upon thewavelength, and the viewer observes both light scattered by Rayleighscattering and light scattered by Mie scattering. It is considered that,for the above reason, synthetic leathers produced using the releasesheet according to the present invention have a matte surface which isjet-black and does not show faded color.

[0041] The specific surface area is preferably 10 to 500 m²/g, morepreferably 100 to 200 m²/g. When the specific surface area is less than1 m²/g, the number of pores present per fine particle is so small thatirregular reflection effect cannot be expected. On the other hand, whenthe specific surface area of the fine particles exceeds 1,000 m²/g, thepore diameter is so small that irregular reflection of light does notoccur. Further, when a coating liquid containing porous fine particleshaving the above size is used, the ingredients and the solvent componentin the coating liquid are moderately absorbed into the pores of the fineparticles. Therefore, even when fine particles in a desired amount areincorporated in the coating liquid, the coatability of the coatingliquid is not deteriorated and an even coating can be formed.

[0042] The fine particles used in the composition for matte layerformation according to the present invention have a mean particlediameter in the range of 1 to 6 μm. The use of the fine particles withparticle diameters in the above defined range can realize a syntheticleather having a matte surface which is best to the touch. The particlediameter of the fine particles is preferably 2 to 5 μm, more preferably2.5 to 3.5 μm. When the particle diameter is less than 1 μm, it isdifficult to perceive the surface as a matte surface. On the other hand,when the particle diameter exceeds 6 μm, hitches causative of the dropof particles are formed on the surface of the matte layer in the releasesheet. Further, since fine particles are precipitated in the coatingliquid for matte layer formation, the stability of the coating liquid isdeteriorated.

[0043] Further, these porous fine particles preferably have been surfacetreated. More preferably, when the thermosetting resin is soluble inwater, the surface treatment is inorganic surface treatment, while, whenthe thermosetting resin is nonaqueous, the surface treatment is organicsurface treatment. The modification of the surface of the fine particleswith an inorganic or organic material can improve the compatibility ofthe fine particles with the thermosetting resin which will be describedlater. In this case, even when the matte layer is formed on thesubstrate, the aggregation of the fine particles can be suppressed. Whena coating liquid is prepared using the surface treated fine particles,the coating liquid has improved fluidity. Therefore, the incorporationof these fine particles in a desired amount in the coating liquid doesnot deteriorate the coatability of the coating liquid.

[0044] Organic materials usable herein include polyethylene waxes,paraffin waxes, and organosilicon compounds. Among them, organosiliconcompounds are particularly preferred.

[0045] The matting agent comprising the porous fine particles ispreferably contained in an amount of 5 to 50% by weight in thecomposition for matte layer formation. When the content of the mattingagent in the composition is less than 5% by weight, the contemplatedmatte layer cannot be formed. On the other hand, when the content of thematting agent in the composition exceeds 50% by weight, the coatabilityof the composition onto the substrate is deteriorated and the formationof an even surface is disadvantageously difficult. The content of thematting agent in the composition is preferably 7 to 20% by weight, morepreferably 10 to 15% by weight.

[0046] Examples of the thermosetting resin constituting the compositionfor matte layer formation according to the present invention includemelamine resins such as alkyd resins, methylol melamine resins, andmethoxymethylol melamine resins. These resins may be used as a propermixture thereof. In order to suppress the so-called “drop of porous fineparticles” in the release sheet, the use of melamine resin is preferred.

[0047] The composition for matte layer formation according to thepresent invention preferably comprises a release agent in addition tothe above ingredients. When the composition contains the release agent,in the production of a synthetic leather using the release sheet, therelease sheet can be easily separated from the synthetic leather.Further, the formed synthetic leather has a good surface state. Therelease agent is not particularly limited, and examples of releaseagents usable herein include silicones, alkyd resins, alkyd-siliconecopolymers, or silicone-modified amino alkyd resins as disclosed inJapanese Patent Laid-Open No. 28242/1990, and mixtures of the abovematerials. The content of the release agent is preferably 0 to 60% byweight, more preferably 30 to 60% by weight. As the content of therelease agent is increased, the synthetic leather can be easilyseparated from the release sheet. A release agent content exceeding 60%by weight, however, causes an excessive lowering in frictionalresistance of the surface of the release sheet which is causative ofwinding loosing of a release sheet roll. Further, in the production of asynthetic leather, when a synthetic leather coating material is coatedonto the release sheet, the coating material is repelled from therelease sheet due to poor wettability of the release sheet by thecoating material.

[0048] Next, the release sheet of the present invention produced usingthe above composition for matte layer formation and the productionprocess thereof will be described.

[0049]FIG. 1 is a typical cross-sectional view showing a firstembodiment of the release sheet for the production of a syntheticleather according to the present invention. The construction of arelease sheet 10 shown in FIG. 1 is such that a smoothing layer 2 isprovided on the upper surface of a substrate 1 and a matte layer 3 isprovided on the smoothing layer 2.

[0050] According to this construction, the smoothness of the substratecan be improved by the smoothing layer. For example, when a materialhaving a relatively rough surface such as paper or a nonwoven fabric isused as the substrate, the provision of a smoothing layer 2 between thesubstrate 1 and the matte layer 3 is preferred. When the surface of thesubstrate is smoothed, a smooth and even matte layer can be formed. As aresult, in the production of a synthetic leather, it is possible toprevent the pattern present on the surface of the substrate fromappearing as spots on the surface of the synthetic leather. Further,after the production of the synthetic leather, the release sheet can beeasily separated from the synthetic leather without increasing thepeeling resistance.

[0051] The smoothing layer can be formed using any composition withoutparticular limitation. An example of a suitable composition forsmoothing layer formation is a composition having the same formulationas the composition for matte layer formation except that the porous fineparticles are absent. This composition can form a smoothing layer whichhas good adhesion to the matte layer and excellent peeling resistance.When the matte layer has a satisfactory thickness, the provision of thesmoothing layer is not always necessary. Since, however, the formationof a thick matte layer results in deteriorated drying properties, thethickness of the matte layer is preferably as thin as possible so far asthe thickness does not adversely affect the formation of fine concavesand convexes 4 on the surface of the matte layer. The formation of athin matte layer, however, sometimes causes surface defects such asspotted dropouts. Therefore, the formation of the smoothing layer ispreferred also from the viewpoint of compensating such defects.

[0052] When paper is used as the substrate, the smoothing layer may be aclay coating. In this case, the thickness of the smoothing layer ispreferably about 20 to 40 μm, more preferably 20 to 30 μm. Since theclay coating can smooth the surface of the paper, a matte layer can beuniformly formed on the paper through the clay coating.

[0053] The composition for smoothing layer formation may contain aleveling agent. The incorporation of the leveling agent in thecomposition for smoothing layer formation can flatten concaves andconvexes formed on the coated face (the surface of the smoothing layerformed on the substrate) with the elapse of time. The incorporation ofthe leveling agent in the composition for smoothing layer formation hassuch an additional effect that the occurrence of orange peel, wrinkling,pinholes, foaming, raising, cracking, cratering and the like on thecoating surface can be prevented to smooth the surface.

[0054] The leveling agent is not particularly limited so far as theleveling agent used does not deteriorate the adhesion of the smoothinglayer to the matte layer formed on the smoothing layer. Leveling agentsusable herein include, for example, silicone resins, such as siliconeoils and silicone-modified resins, and, in addition, polymeric materialscalled organic polymeric leveling agents. For example, when a siliconeoil is used as the leveling agent, the silicone oil gathers on thesurface of the coating to form a kind of a barrier layer. Therefore, theevaporation of the solvent becomes uniform, and the surface tension ofthe coating is lowered, leading to favorable effects. Since, however,the sole use of the silicone oil deteriorates post-adhesion, thecombined use of the organic polymeric leveling agent and the siliconeoil is preferred from the viewpoint of reducing the amount of thesilicone oil added.

[0055] The organic polymeric leveling agent is not particularly limitedso far as the organic polymeric leveling agent can be dissolved in theresin solution to lower the surface tension of the resolution and doesnot lower the post-adhesion. Examples of suitable organic polymericleveling agents usable herein include polyvinyl butyral andlow-molecular weight cellulose. The use of a mixture of these polymericmaterials increases the viscosity of the coating liquid and suppressesrising of foams derived from dynamic viscosity and thus results in theformation of a smooth coating surface. The “post-adhesion” as usedherein refers to the adhesion between the smoothing layer and the mattelayer. When this adhesion is low, in the production of a syntheticleather, upon the separation of the release sheet from the syntheticleather, the matte layer, together with the synthetic leather, isdisadvantageously separated from the smoothing layer.

[0056] For example, internally curable silicone resins orfluorocopolymer resins may also be used as the leveling agents, althoughthese resins are inferior to the above polymeric leveling agents in thepost-adhesion.

[0057] Internally curable silicone resins include silicone acrylates,and specific examples thereof include acrylsilanes and methacrylsilanes,acrylsilicones and methacrylsilicones, and phenylsilicone acrylate andm-phenylsilicone acrylate. More specific examples thereof includeacrylsilanes such as acryloxypropylmethyldimethoxysilane andacryloxypropyltrimethoxysilane, and methacrylsilanes such asmethacryloxypropylmethyldimethoxysilane, andmethacryloxypropyltrimethoxysilane.

[0058] Further, the so-called “surfactant” or the like may be used asthe organic polymeric leveling agent. Since, however, this function tolower the surface tension, solvents used are limited and, for example,aqueous coating, such as alcoholic or emulsion coating, is necessary.

[0059] When organic solvent systems are used, the above-describedpolymeric materials, silicone-modified copolymer resins, fluorocopolymerresins and the like may be used as the organic polymeric leveling agent.Specific examples thereof include Chaline Series manufactured by NissinChemical Industry Co., Ltd. Further, for example, Talen, Flowlen, andPolyflow, which are organic copolymers such as low-molecular weightcellulose, manufactured by Kyoeisha Chemical Co., Ltd. are alsopreferred.

[0060] Two or more organic polymeric leveling agents can also be used incombination. For example, the addition of an internally curable siliconein addition to a low-molecular weight cellulose can also provide goodresults.

[0061] The amount of the organic polymeric leveling agent added ispreferably about 0.01 to 3% by weight based on the composition forsmoothing layer formation. If the amount of the organic polymericleveling agent added is less than 0.01% by weight, then the levelingeffect cannot be attained, while if it exceeds 3% by weight, thepost-adhesion is disadvantageously lowered.

[0062]FIG. 2 shows a second embodiment of the release sheet for theproduction of a synthetic leather according to the present invention. Asshown in FIG. 2, the matte layer 3 has a multilayer structure of two ormore layers, i.e., releasable resin layers (3 a and 3 b), and, among thelayers constituting the multilayered matte layer, each of all thereleasable resin layers 3 a except for at least the layer 3 b in contactwith the surface of the substrate contains a release agent comprising asilicone-modified resin or a silicone-containing resin composition. Inthis case, as the layer is closer to the surface of the matte layer, thecontent of the release agent is increased.

[0063] When the formation of a matte layer having high smoothness bycoating the resin with a silicone resin or the like added thereto anddrying the coating is contemplated, the resin should be coated to alarge thickness. Coating of the resin to a large thickness, however,deteriorates the drying properties of the coating. Acceleration of thedrying by strong heating or the like for solving this problemdeteriorates the smoothness of the matte layer. A solution to thisproblem is to form a multilayered matte layer. When the resin for mattelayer formation contains a silicone-modified resin or a silicone,however, mere stacking of coatings formed using coating liquids havingthe same composition poses a problem that the receptivity or adhesion tolater stacked layers for constituting the matte layer is deteriorated.

[0064] In the release sheet according to the present invention, asdescribed above, the formation of a matte layer having a multilayerstructure of releasable resin layers is advantageous in that, even whenthe formation of a thick matte layer is contemplated due tounsatisfactory smoothness of the substrate, the thickness of each of thelayers constituting the matte layer can be made small and, in addition,the lower release layer can improve the smoothness, whereby a smoothmatte layer can be efficiently formed without sacrificing the dryingproperties. Further, among the layers constituting the multilayeredmatte layer, all the releasable resin layers except for at least theinnermost layer, that is, the outer releasable resin layers, contain asilicone-modified resin or silicone, and, in addition, as the releasableresin layer is closer to the outer surface of the matte layer, thecontent of the silicone-modified resin or silicone in the releasableresin layer is higher. Therefore, the adhesion between the releasableresin layers is not deteriorated.

[0065] What is required of the innermost layer constituting themultilayered matte layer is only to function as a smoothness improvinglayer, and the releasability is not required of the innermost layer.Therefore, the addition of the silicone-modified resin or silicone asthe release agent to the innermost releasable resin layer is notnecessary. That is, in the innermost releasable resin layer, the mixingratio of the silicone-modified resin or silicone may be 0 (zero). Since,however, good leveling is necessary, the silicone-modified resin orsilicone may be used as a leveling agent in a limited minor amount. Whenthe silicone-modified resin or silicone is used as the leveling agent,the silicone-modified resin or silicone may be used in combination withthe above leveling agent, or alternatively other leveling agents may beused instead of the silicone-modified resin or silicone.

[0066] The third embodiment of the release sheet for the production of asynthetic leather according to the present invention comprises: a mattelayer having fine concaves and convexes on its surface; and a substratefor supporting the matte layer, said matte layer comprising a releasableresin layer, a releasable transparent resin being provided so as to stayon the bottom of the concaves in the concave-convex portion. The use ofthe release sheet having a matte layer in which a transparent resinstays on the bottom of the concaves in the concave-convex portion canrealize the production of a synthetic leather which is finer to thetouch, that is, has the so-called “peach skin-like” feel. Further, whenthe transparent resin is used, synthetic leathers with different colorsor with a light color can be continuously produced without the influenceof the color of the previously produced synthetic leather and therelease sheet can be repeatedly used with safety.

[0067]FIG. 3 is a typical cross-sectional view of a principal partillustrating the step of allowing a part of a coated transparentsynthetic resin layer to stay on the bottom of the concaves in the fineconcave-convex portion on the surface of the releasable resin layer inthe release sheet according to the present invention.

[0068] After a matte layer 3 is formed on a substrate 1, a transparentsynthetic resin liquid is coated onto the matte layer 3 to form acoating which is then heat dried to form a transparent synthetic resinlayer 5. The transparent synthetic resin layer 5 is then separated fromthe release sheet 10. Thus, a broken transparent synthetic resin 5′stays on the bottom of the concaves in the fine concaves and convexes 4of the matte layer 3.

[0069] More specifically, a transparent synthetic resin liquid is coatedonto the surface of the matte layer 3 in the release sheet 10. In thiscase, the synthetic resin liquid also enters the concaves in the fineconcaves and convexes. The coating is brought into a film, for example,by heat drying to form a transparent synthetic resin layer 5. When thetransparent synthetic resin layer 5 is then separated from the releasesheet 10, the transparent synthetic resin layer 5, which has entered theconcaves in the fine concaves and convexes, is broken partway becausethe peeling resistance at the time of separation is larger than thebreaking strength. As a result, a transparent synthetic resin 5′ remainsunremoved on the bottom of the concaves (see FIG. 4). The broken face ofthe transparent synthetic resin 5′ remaining unremoved is in anirregular and fine concave-convex form. Therefore, the whole surface ofthe matte layer 2 is in the form of fine concaves and convexes withdifferent finesses which are suitable for imparting a peach skin-likefeel to the surface of the synthetic leather. Accordingly, when asynthetic leather is produced using this release sheet, a peachskin-like feel can be imparted to the surface of the synthetic leather.

[0070] The resin used is not particularly limited. However, a part ofthe resin, which has entered the concaves, should be broken with properbreaking strength. To this end, for example, a resin composition havingthe same formulation as the resin composition for the formation of askin layer in a synthetic leather except for the absence of the colorantcan be suitably used. Specific examples of resin compositions usableherein include a polyurethane composition in a paste form for apolyurethane leather (hereinafter referred to simply as “PU leather”),in which additives other than the colorant may be contained and thesolid content is about 20 to 50% by weight, and a polyvinyl chloridecomposition for a PVC leather, in which a PVC sol is generally used and,likewise, additives other than the colorant, for example, a plasticizerand a stabilizer, may be contained. The above synthetic resin may becoated by a conventional coating method such as knife coating, rollcoating, or gravure coating. As shown in FIG. 5, the smoothing layer 2as described above may also be provided between the matte layer and thesubstrate.

[0071] Papers such as kraft papers, wood free papers, and cast coatedpapers may be used as the substrate for supporting the smoothing layerand the matte layer. Other materials usable as the substrate include:films of plastics, for example, polyesters such as polyethyleneterephthalate and polyethylene naphthalate, polyamides such as variousnylons, and polypropylene; synthetic papers; metal foils; woven fabrics;and nonwoven fabrics. These materials may be used solely or as a properlaminate of two or more of them.

[0072] The substrate preferably has a surface resistivity (Ω) of notmore than 1.0×10¹². In particular, preferably, the substrate contains anorganic polymeric conductive agent and/or an inorganic conductive agent,or has, on any one side thereof, a coating of the organic polymericconductive agent and/or the inorganic conductive agent, and the contentof the conductive agent is in the range of 0.05 to 3.00 g/m² based onthe substrate.

[0073] When the resistivity of the substrate is in the above definedrange, antistatic effect can be attained. That is, at the time of theformation of the matte layer and at the time of the production of asynthetic leather using the release sheet, cracking of the surface ofthe matte layer or of the synthetic leather by the occurrence of staticelectricity can be prevented.

[0074] A possible formulation of main materials for constituting thesubstrate is as follows. Regarding a pulp formulation, bleached kraftpulp of a broad-leaved tree (L-BKP) and bleached kraft pulp of aneedle-leaved tree (N-BKP) are used as main pulp fibers, and waste stuffor waste paper pulp is properly mixed thereinto. Further, internalsizing agents, cationized starches, and antifoaming agents, such asfatty esters and special paraffins, and the like may be used asadditives. In a substrate size press process, a size press liquidcontaining a corn starch, a surface sizing agent, a conductive agent andthe like is coated onto a base paper. In this size press process, thesize press liquid is coated on both sides of the substrate and is alsoimpregnated into the substrate.

[0075] Conductive agents usable herein are organic polymeric conductiveagents and/or inorganic conductive agents. Organic polymeric conductiveagents include: nonionic polymers such as polyvinyl alcohol,polyacrylamide, and polyethylene glycol; anionic polar group-containingpolymers such as sulfonated styrene resin; and cationic polymers, forexample, quaternary ammonium salts such as quaternary ammonium chloride.Inorganic conductive agents include calcium oxide, sodium aluminate,zinc oxide, tin oxide, calcium chloride, lithium chloride, potassiumchloride, magnesium chloride, sodium chloride, and carbon black.

[0076] The content of the conductive agent or the coverage of theconductive agent on the surface of the substrate may be in the range of0.05 to 3.0 g/m², preferably in the range of 0.2 to 2.0 g/m². When theamount of the conductive agent is less than 0.05 g/m², the surfaceresistivity of the substrate is likely to exceed 1.0×10¹² Ω and,consequently, the antistatic effect is unsatisfactory. For this reason,at the time of the formation of the matte layer or at the time of theproduction of a synthetic leather using this type of release sheet,cracking occurs in the matte layer or the synthetic leather due to thegeneration of static electricity. On the other hand, when the amount ofthe conductive agent exceeds 3.0 g/m², a further improvement in theantistatic effect cannot be expected and, further, in this case, thematerial cost is disadvantageously increased.

[0077] On the other hand, when a plastic film or a metal foil is used asthe substrate, the provision of the smoothing layer is unnecessarybecause the surface of the plastic film or metal foil is generallysmooth. In some cases, however, the adhesion to the matte layer isunsatisfactory. In this case, the surface of the substrate may besubjected to easy-adhesion treatment such as corona discharge treatmentor ozone treatment, or alternatively a primer coating or the like may beapplied to the surface of the substrate.

[0078] A smoothing layer and a matte layer are formed on the substrate.In the formation of the smoothing layer, the composition for smoothinglayer formation is provided as a coating liquid, and the coating liquidis coated, for example, by a coating method such as bar coating, airdoctor coating, blade coating, squeeze coating, air knife coating, rollcoating, gravure coating, transfer coating, Komma coating, smoothingcoating, microgravure coating, reverse roll coating, multiroll coating,dip coating, rod coating, kiss coating, gate roll coating, drop curtaincoating, slide coating, fountain coating, or slit die coating. After thecoating liquid is coated, the coating is dried and solidified to form asmoothing layer. Next, the composition for matte layer formation isprovided as a coating liquid and may be coated in the same manner asdescribed above to form a matte layer.

[0079] In the release sheet thus produced, the thickness of thesmoothing layer is preferably 0.5 to 10 g/m² in terms of coverage afterdrying of the coating. If the thickness of the smoothing layer is lessthan 0.5 g/m², then the contemplated effect of the smoothing layercannot be expected. On the other hand, a thickness of more than 10 g/m²causes a lowering in drying speed and processing speed and is alsodisadvantageous from the viewpoint of cost.

[0080] The thickness of the matte layer is preferably in the range of1.0 to 20 g/m² in terms of coverage after drying of the coating. If thethickness of the matte layer is less than 1.0 g/m², then the formationof an even coating is difficult. Coating to a larger thickness ispreferred from the viewpoint of providing a satisfactorily matte surfaceor from the viewpoint of releasability. A thickness exceeding 20 g/m²,however, causes a lowering in drying speed and processing speed and isalso disadvantageous from the viewpoint of cost.

[0081] In the release sheet thus obtained, a fine concave-convex portion4 is formed on the surface of the matte layer, and the arithmetical meanroughness (Ra) of the matte surface is 0.5 to 15 μm. More preferably,the mean spacing of profile irregularities (concaves and convexes) (Sm)in the concave-convex portion on the surface of the matte layer is 0.5to 10 μm.

[0082] In the release sheet in which a transparent resin is provided soas to stay in the concaves, preferably, the concave-convex portion hasan arithmetical mean roughness (Ra) of 0.5 to 15 μm, the mean spacing ofprofile irregularities (concaves and convexes) (Sm) in theconcave-convex portion is 0.5 to 10 μm, and the mean inclination (θa) ofthe concaves and convexes is 45 degrees≦θa<90 degrees. The arithmeticalmean roughness (Ra) of the fine concaves and convexes and the meanspacing of profile irregularities (concaves and convexes) (Sm) arevalues measured based on JIS B 0601-1994 “Surface roughness—Definitionsand designation” under the following measuring conditions.

[0083] Measuring Conditions

[0084] Tip radius of stylus: load 5 μm: cut-off value 4 mN: standardvalue described in Table 1 is selected.

[0085] Reference length: standard value described in Table 2 isselected.

[0086] Measuring instrument: surface roughness measuring deviceSuftest-201, manufactured by MITUTOYO CORPORATION TABLE 1 Cut-off valueλc, Evaluation length Ra range, μm mm Ln, mm 0.006 < Ra ≦ 0.02 0.08 0.4 0.02 < Ra ≦ 0.1 0.25 1.25  0.1 < Ra ≦ 2.0 0.8 4.0  2.0 < Ra ≦ 10.0 2.512.5  10.0 < Ra ≦ 80.0 8.0 40.0

[0087] TABLE 2 Reference length Evaluation length Sm range, μm L, mm Ln,mm 0.013 < Sm ≦ 0.04 0.08 0.4  0.04 < Sm ≦ 0.13 0.25 1.25  0.13 < Sm ≦0.4 0.8 4.0  0.4 < Sm ≦ 1.3 2.5 12.5  1.3 < Sm ≦ 4.0 8.0 40.0

[0088] A synthetic leather can be produced using the above release sheetby conventional paste coating method (vinyl chloride leather method;hereinafter referred to as “PVC leather method”) or dry method(polyurethane leather method; hereinafter referred to as “PU leathermethod”).

[0089] Specifically, a synthetic leather with fine concaves and convexesbeing formed on the surface thereof can be produced by coating a resincomposition for a skin layer in a synthetic leather onto the surface ofa matte layer in the release sheet, drying the coating by heating toform a film as the skin layer, then laminating a backing fabric onto theskin layer with the aid of an adhesive, drying and aging the assembly,and then separating the release sheet.

[0090] For example, in the formation of the PVC leather, a PVC paste,wherein polyvinyl chloride is used as a main component and aplasticizer, a foaming agent, a stabilizer, a colorant and the like havebeen properly added to polyvinyl chloride, may be used as the resincomposition for a skin layer in the synthetic leather. In the formationof the PU leather, a composition having a solid content of about 20 to50% by weight prepared by optionally adding a colorant and otheradditives to a polyurethane solution may be used. The above compositionfor skin layer formation may be coated by conventional coating meanssuch as knife coating, roll coating, reverse roll coating, or gravurecoating.

[0091] The synthetic leather produced by the above method is a mattesynthetic leather which has a matte surface with a high level ofjet-blackness without the practice of embossing, raising or the like.Further, since the surface shape of the release sheet is transferredonto the surface of the synthetic leather, the surface of the syntheticleather has an arithmetical roughness (Ra) of 0.5 to 15 μm and aglossiness in the range of 0.5 to 10% as measured in 85-degreeincidence/85-degree reflection.

[0092] Further, the synthetic leather produced using the release sheetwith a transparent resin staying in the concave portion of the mattelayer has on its surface a releasable transparent resin layer.Therefore, the surface of the synthetic leather has a peach skin-likefeel and, at the same time, is less likely to be soiled and, even whensoiled, can be easily cleaned because the soil can be easily removed.

[0093] The following examples further illustrate the present inventionbut are not intended to limit it. It should be noted that any technicalidea, which has constitution and function and effect substantiallyidentical to that described in claims of the present invention, areembraced within the technical scope of the present invention.

EXAMPLES Examples 1 to 3

[0094] A cast coated paper having a basis weight of 155 g/m²manufactured by Oji Paper Co., Ltd. was provided as a substrate. Acoating liquid for smoothing layer formation having the followingcomposition was roll coated onto the cast coated face at a coverage of 5g/m² on a dry basis, and the coating was dried by heating at 160° C. forone min or longer to form a smoothing layer.

Composition of Coating Liquid for Smoothing Layer Formation

[0095] Melamine resin (Melan 28, manufactured 220 pts. wt. by HitachiChemical Co., Ltd.) Alkyd resin (Phthalkyd 133-60, 100 pts. wt.manufactured by Hitachi Chemical Co., Ltd.) Acid catalyst(p-toluenesulfonic acid) 8.4 pts. wt. Solvent (toluene/n-butyl alcohol:980 pts. wt. weight ratio = 1/1)

[0096] Next, coating liquids for matte layer formation having thefollowing compositions containing various types of silica shown in Table3 were roll coated onto the smoothing layer at a coverage of 10 g/m² ona dry basis, and the coatings were dried by heating at 180° C. for onemin or longer to form matte layers. Thus, release sheets of Examples 1to 3 were prepared.

Coating Liquid for Matte Layer Formation

[0097] Methylolated melamine resin 50 pts. wt. Silicone-modified alkydresin 50 pts. wt. Acid catalyst (p-toluenesulfonic 4.2 pts. wt. acid)Porous fine particles (silica: 10 pts. wt. see Table 2) Solvent(toluene/n-butyl alcohol: 500 pts. wt. weight ratio = 1/1)

[0098] The coating liquids for matte layer formation, when coated on thesmoothing layer, could be evenly coated without cissing, and, uponcuring by heating, each of the coatings could form a smoothing layerhaving good adhesion to the matte layer. FIG. 6 shows an electronphotomicrograph of the surface of the release sheet produced in Example1.

[0099] For the release sheets of Examples 1 to 3 thus prepared, thearithmetical mean roughness (Ra) of the surface of the matte layer isshown in Table 3.

[0100] The following two synthetic leathers, a PVC leather and a PUleather, were prepared using the release sheets of Examples 1 to 3 thusobtained.

[0101] Preparation of Matte PVC Leather

[0102] A PVC composition (paste), for the formation of a skin layer in asynthetic leather, prepared by mixing 100 parts by weight of a PVC resin(molecular weight 1,000), 60 parts by weight of a plasticizer DOP, 5parts by weight of a foaming agent, 2.5 parts by weight of a stabilizer,and 15 parts by weight of a colorant (SEIKASEVEN NET-5794 Black,manufactured by Dainichiseika Color & Chemicals Manufacturing Co., Ltd.)together was knife coated onto the surface of the matte layer in therelease sheet of Example 1 at a coverage of 150 g/m² on a dry basis. Thecoating was dried by heating at 190 to 200° C. for 2 min or longer.Thereafter, a backing fabric was applied onto the dried coating with theaid of an adhesive, and the laminate was dried and aged. The releasesheet was then separated and removed to prepare a PVC leather 1.

[0103] The PVC leather 1 thus obtained could be easily separated fromthe release sheet without significant peeling resistance and had a mattesurface with a high level of jet-blackness. The glossiness of the PVCleather thus obtained was measured under conditions of 85-degreeincidence/85-degree reflection. The results of the measurement ofsurface glossiness of the PVC leather are shown in Table 3. FIG. 7 showsan electron photomicrograph of the surface of the PVC leather 1 preparedin Example 1.

[0104] Preparation of Matte PU Leather

[0105] A PU composition (paste), for the formation of a skin layer in asynthetic leather, prepared by mixing 100 parts by weight ofpolyurethane (Resamine NE-8811, manufactured by Dainichiseika Color &Chemicals Manufacturing Co., Ltd.), 15 parts by weight of a colorant(SEIKASEVEN NET-5794 Black, manufactured by Dainichiseika Color &Chemicals Manufacturing Co., Ltd.), 25 parts by weight of toluene, and25 parts by weight of isopropyl alcohol together was knife coated ontothe surface of the matte layer in the release sheet of Example 1 at acoverage of 150 g/m² on a dry basis. The coating was dried by heating at100 to 120° C. for 2 min or longer. Thereafter, a backing fabric wasapplied onto the dried coating with the aid of an adhesive, and thelaminate was dried and aged. The release sheet was then separated andremoved to prepare a PU leather 1.

[0106] The PU leather 1 thus obtained could be easily separated from therelease sheet without significant peeling resistance and had a mattesurface with a high level of jet-blackness. Even after the repetition ofthe preparation of the PU leather 1 three times or more, the leather hadthe same matte surface as in the first preparation of the syntheticleather.

Comparative Examples 1 and 2

[0107] Release sheets were prepared in the same manner as in Example 1,except that fine particles shown in Table 3 were used instead of theporous fine particles used in the coating liquid for matte layerformation in Example 1. Synthetic leathers were prepared in the samemanner as in Example 1, except that the release sheets prepared justabove were used. The arithmetical mean roughness (Ra) of the releasesheets thus obtained and the glossiness of the PVC leathers producedusing the release sheets were measured, and the results are shown inTable 3. TABLE 3 Fine particles (silica) Release sheet Particlediameter, Specific surface Surface Surface roughness PVC leather μmarea, m²/g treatment Ra, μm Glossiness, % Ex. 1 2.5 150 Organic 2.0 1.2Ex. 2 1.0 200 Organic 1.0 1.1 Ex. 3 10.0 60 Organic 10.2 1.6 Comp. Ex. 12.5 1500 Organic 2.1 17.0 Comp. Ex. 2 2.5 0.1 Inorganic 1.7 20.0

Example 4

[0108] Preparation of PVC Leather Having Combination of Matte Tone WithPeach Skin Tone

[0109] A release sheet 4 was prepared in quite the same manner as inExample 1, except that a mixture of 10 parts by weight of silica, whichhad been subjected to organic surface treatment and had a mean particlediameter of 5.2 μm (specific surface area: 340 to 350 m²/g) (SYLYSIA456, manufactured by Fuji Silysia Chemical Ltd.), with 10 parts byweight of silica which had been subjected to organic surface treatmentand had a mean particle diameter of 2.5 μm (specific surface area: 340to 350 m²/g) (SYLYSIA 436, manufactured by Fuji Silysia Chemical Ltd.)was used as the porous fine particles. Skin layers for a syntheticleather were formed on the surface of the matte layer in the releasesheet 4 as follows. At the outset, a PVC composition (paste) prepared bymixing 100 parts by weight of PVC (molecular weight 1,000), 60 parts byweight of a plasticizer (DOP), and 1 (one) part by weight of awater-dispersed silicone release agent (amino-modified silicone)together was gravure coated at a coverage of 2 g/m² on a dry basis, andthe coating was dried. Next, a PVC composition (paste), for skin layerformation in a synthetic leather, prepared by mixing 100 parts by weightof a PVC resin (molecular weight 1,000), 60 parts by weight of aplasticizer DOP, 5 parts by weight of a foaming agent, 2.5 parts byweight of a stabilizer, and 15 parts by weight of a colorant (SEIKASEVENNET-5794 Black, manufactured by Dainichiseika Color & ChemicalsManufacturing Co., Ltd.) together was knife coated thereon at a coverageof 150 g/m² on a dry basis, and the coating was then dried by heating at190 to 200° C. for 2 min or longer. Thereafter, a backing fabric wasapplied onto the dried coating with the aid of an adhesive, and thelaminate was dried and aged. The release sheet was then separated andremoved to prepare a PVC leather 4.

[0110] The PVC leather 4 thus obtained had a releasable thin transparentPVC resin layer on its surface, and the surface thereof was a fine touchsurface having a combination of a matte tone with a peach skin tone.After the separation of the release sheet, the PVC transparent resinremained unremoved on the bottom of the concaves in the fineconcave-convex portion on the surface of the release sheet, and thecolored PVC (PVC leather side) resin was not transferred onto and wasabsent on the release sheet side.

[0111] The preparation of PVC leather with different colors was repeatedfive times using the release sheet in Example 4 in the same manner as inExample 4. As a result, the release sheet could be easily separated fromthe synthetic leather without significant peeling resistance. Further,since the release sheet could be continuously used without the transferof the colored PVC resin in the leather skin layer onto the releasesheet, PVC leathers having an excellent matte surface could beefficiently produced.

[0112] Example 5

[0113] Preparation of PU Leather Having Combination of Matte Tone WithPeach Skin Tone

[0114] Skin layers for a synthetic leather were formed on the surface ofthe matte layer in the same release sheet as prepared in Example 4 asfollows. At the outset, a coating liquid prepared by mixing 100 parts byweight of a polyurethane composition (Resamine NE-8811, manufactured byDainichiseika Color & Chemicals Manufacturing Co., Ltd.), 0.5 part byweight of a silicone release agent (amino-modified silicone), 0.5 partby weight of epoxy-modified silicone, and 25 parts by weight of tolueneand 25 parts by weight of isopropyl alcohol (hereinafter referred to as“IPA”) as solvents together was gravure coated on the surface of thematte layer at a coverage of 1.5 g/m² on a dry basis, and the coatingswere then dried. Next, a PU composition (black colored paste), for theformation of a skin layer in a synthetic leather, prepared by mixing 100parts by weight of polyurethane (Resamine NE-8811, manufactured byDainichiseika Color & Chemicals Manufacturing Co., Ltd.), 15 parts byweight of a colorant (SEIKASEVEN NET-5794 Black, manufactured byDainichiseika Color & Chemicals Manufacturing Co., Ltd.), 25 parts byweight of toluene, and 25 parts by weight of IPA together was knifecoated thereon at a coverage of 150 g/m² on a dry basis, and the coatingwas dried by heating at 100 to 120° C. for 2 min or longer. Thereafter,a backing fabric was applied onto the dried coating with the aid of anadhesive, and the laminate was dried and aged. The release sheet wasthen separated and removed to prepare a PU leather 5.

[0115] The PU leather 5 thus obtained had a releasable thin transparentPU resin layer on its surface, and, as with the synthetic leatherprepared in Example 4, the PU leather 5 had a surface with a combinationof a matte tone having a high level of jet-blackness with a peach skintone. After the separation of the release sheet, the PU transparentresin remained unremoved on the bottom of the concaves in the fineconcave-convex portion on the surface of the release sheet, and thecolored PU (PU leather side) resin was not transferred onto and wasabsent on the release sheet side.

[0116] The preparation of PU leather with different colors was repeatedfive times using the release sheet in Example 5 in the same manner as inExample 5. As a result, the release sheet could be easily separated fromthe synthetic leather without significant peeling resistance. Further,since the release sheet could be continuously used without the transferof the colored PU resin in the leather skin layer onto the releasesheet, PU leathers having an excellent matte surface could beefficiently produced.

Example 6

[0117] A release sheet 6 was prepared in quite the same manner as inExample 1, except that 40 parts by weight of silica, which had beensubjected to organic surface treatment and had a mean particle diameterof 5.2 μm (specific surface area: 340 to 350 m²/g) (SYLYSIA 456,manufactured by Fuji Silysia Chemical Ltd.), was used as the porous fineparticles.

[0118] Fine concaves and convexes formed on the surface of the mattelayer in the release sheet 6 had an arithmetical mean roughness (Ra) of0.54 μm, a mean profile irregularity spacing (Sm) of 9 μm, and a meaninclination (θa) of 47 degrees and were good as fine concaves andconvexes for imparting peach skin-like appearance and touch to thesurface of the synthetic leather.

[0119] A PU leather with a skin layer having a two-layer structure of areleasable thin transparent resin layer provided on the surface side anda colored resin layer provided on the inner layer side was prepared asfollows. At the outset, a coating liquid prepared by mixing 100 parts byweight of a polyurethane composition (Resamine NE-8811, manufactured byDainichiseika Color & Chemicals Manufacturing Co., Ltd.), 0.5 part byweight of a silicone release agent (amino-modified silicone), 0.5 partby weight of epoxy-modified silicone, and 25 parts by weight of tolueneand 25 parts by weight of IPA as solvents together was gravure coated onthe surface of the matte layer in the release sheet 6 at a coverage of2.0 g/m² on a dry basis, and the coatings were then dried. Next, a PUcomposition (red colored paste), for the formation of a skin layer in asynthetic leather, prepared by mixing 100 parts by weight ofpolyurethane (Resamine NE-8811, manufactured by Dainichiseika Color &Chemicals Manufacturing Co., Ltd.), 15 parts by weight of a colorant(SEIKASEVEN NET-5194 Red, manufactured by Dainichiseika Color &Chemicals Manufacturing Co., Ltd.), 25 parts by weight of toluene, and25 parts by weight of IPA together was knife coated thereon at acoverage of 150 g/m² on a dry basis, and the coating was dried byheating at 100 to 120° C. for 2 min or longer. Thereafter, a backingfabric was applied onto the dried coating with the aid of an adhesive,and the laminate was dried and aged. The release sheet was thenseparated and removed to prepare a PU leather 6.

[0120] In the PU leather 6 thus obtained, the skin layer had such aconstruction that a releasable thin transparent PU resin layer wasprovided on the upper surface of a colored PU resin layer. By virtue ofthis construction, the PU leather 6 had unique soft color impression andhad good peach skin-like appearance and feel. After the separation ofthe release sheet, the PU transparent resin remained unremoved on thebottom of the concaves in the fine concave-convex portion on the surfaceof the release sheet, and the colored PU (PU leather side) resin was nottransferred onto and was absent on the release sheet side.

[0121] The preparation of PU leather with different colors was repeatedfive times using the release sheet in Example 5 in the same manner as inExample 5. As a result, the release sheet could be easily separated fromthe synthetic leather without significant peeling resistance. Further,since the release sheet could be continuously used without the transferof the colored PU resin in the leather skin layer onto the releasesheet, PU leathers having an excellent matte surface could beefficiently produced.

What is claimed is:
 1. A composition for matte layer formation suitable for the production of a synthetic leather, said composition comprising a thermosetting resin and a matting agent as indispensable components, said matting agent comprising one or at least two types of organic or/and inorganic porous fine particles, said porous fine particles having a mean particle diameter in the range of 0.5 to 20 μm and a specific surface area in the range of 1 to 1000 m²/g.
 2. The composition according to claim 1, wherein said porous fine particles have been surface treated and have been homogeneously dispersed in the composition for matte layer formation.
 3. The composition according to claim 2, wherein, when the thermosetting resin is soluble in water, the surface treatment is inorganic surface treatment, while, when the thermosetting resin is nonaqueous, the surface treatment is organic surface treatment.
 4. The composition according to claim 1, wherein the content of the porous fine particles in the composition for matte layer formation is 5 to 50% by weight.
 5. The composition according to claim 1, wherein the porous fine particles are selected from silica, calcium carbonate, talc, and a mixture containing at least one of said materials.
 6. The composition according to claim 1, which further comprises a release agent.
 7. A release sheet for the production of a synthetic leather, said release sheet comprising: a matte layer formed by coating the composition for matte layer formation according to any one of claims 1 to 6; and a substrate for supporting the matte layer, said matte layer having a fine concave-convex portion on its surface, said concave-convex portion having an arithmetical mean roughness (Ra) of 0.5 to 15 μm.
 8. A release sheet for the production of a synthetic leather, said release sheet comprising: a matte layer having fine concaves and convexes on its surface; and a substrate for supporting the matte layer, said matte layer comprising a releasable resin layer, a releasable transparent resin being provided so as to stay on the bottom of the concaves in the concave-convex portion.
 9. The release sheet according to claim 8, wherein said concave-convex portion has an arithmetical mean roughness (Ra) of 0.5 to 15 μm, the mean spacing of profile irregularities (concaves and convexes) (Sm) in the concave-convex portion is 0.5 to 10 μm, and the mean inclination (θa) of the concaves and convexes is 45 degrees≦θa<90 degrees.
 10. The release sheet according to claim 8, wherein the releasable resin layer has been formed by coating the composition for matte layer formation according to any one of claims 1 to
 6. 11. The release sheet according to claim 7 or 8, wherein a smoothing layer is provided between the matte layer and the substrate.
 12. The release sheet according to claim 11, wherein the smoothing layer has been formed using a composition having the same formulation as the composition for matte layer formation according to claim 1 except that the porous fine particles are absent in the composition.
 13. The release sheet according to claim 11, wherein the smoothing layer further comprises a leveling agent.
 14. A release sheet for the production of a synthetic leather, said release sheet comprising: a matte layer formed by coating the composition for matte layer formation according to claim 6; and a substrate for supporting the matte layer, wherein said matte layer is a releasable resin layer having a multilayer structure of at least two layers, all the releasable resin layers constituting the multilayered matte layer except for at least the layer in contact with the surface of the substrate contain a release agent comprising a silicone-modified resin or a silicone-containing resin composition, and the content of the release agent is larger as the releasable resin layer is closer to the surface of the matte layer.
 15. The release sheet according to claim 14, wherein all the releasable resin layers constituting the multilayered matte layer except for at least the layer in contact with the surface of the substrate further comprises a leveling agent.
 16. The release sheet according to claim 7, 8, or 14, wherein the substrate has a surface resistivity (Ω) of not more than 1.0×10¹².
 17. The release sheet according to claim 7, 8, or 14, wherein said substrate contains an organic polymeric conductive agent and/or an inorganic conductive agent, or has, on any one side thereof, a coating of the organic polymeric conductive agent and/or the inorganic conductive agent, and the content of the conductive agent is in the range of 0.05 to 3.00 g/m² based on the substrate.
 18. A synthetic leather produced by using the release sheet according to claim 7, 8, or
 14. 19. The synthetic leather according to claim 18, wherein the skin as the outermost layer in the synthetic leather is a transparent resin layer.
 20. The synthetic leather according to claim 19, wherein the transparent resin layer is releasable.
 21. The synthetic leather according to claim 18, which has been produced substantially without embossing or/and raising.
 22. A synthetic leather produced by using a release sheet, said synthetic leather having a surface arithmetical roughness (Ra) of 0.5 to 15 μm and a 85-degree glossiness of 0.5 to 10%. 